Context modeling constraints for block differential pulse-code modulation

ABSTRACT

A method of video encoding performed in a video encoder is provided. In the method, context modeling is performed to determine a context model for each of a number of bins of syntax elements corresponding to residues of a region of a transform skipped block in a coded picture. The transform skipped block is coded with Block Differential Pulse-code Modulation (BDPCM) and divided into a plurality of regions. The number of the bins of syntax elements being context coded does not exceed a maximum number of context coded bins set for the region. The maximum number of context coded bins is determined based on a comparison between a threshold and a number of quantized residues in the region. A bit stream including coded bits of the bins of syntax elements is generated based on the determined context models.

INCORPORATION BY REFERENCE

The present application is a continuation of U.S. application Ser. No.16/710,899 filed on Dec. 11, 2019, which claims the benefit of priorityto U.S. Provisional Application No. 62/785,056, “Constraints for ContextModeling and Deblocking Filter in Block Differential Pulse-CodeModulation” filed on Dec. 26, 2018. The disclosures of the priorapplications are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016).

Referring to FIG. 1 , a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videocoding at a decoder. In an embodiment, a method of video coding at adecoder is provided. In the method, a bit stream including coded bits ofbins of syntax elements is received. The syntax elements correspond toresidues of a region of a transform skipped block in a coded picture.Context modeling is performed to determine a context model for each of anumber of the bins of syntax elements of the region. The number of thebins of syntax elements that are context coded does not exceed a maximumnumber of context coded bins set for the region. The coded bits of thenumber of the bins of syntax elements are decoded based on thedetermined context models.

In an embodiment, the number of the bins of syntax elements that arecontext coded is less than or equal to a total number of the bins ofsyntax elements for the region of the transform skipped block.

In an embodiment, the maximum number of context coded bins for theregion of the transform skipped block is B×A, where B is a positivenumber and A is a number of quantized residues in the region.

In an embodiment, the coded bits of the remaining total number of thebins of syntax elements that are not context coded for the region of thetransform skipped block are decoded based on an equal probability model.

In an embodiment, B is an integer.

In an embodiment, B is a fractional number.

In an embodiment, B is set according to A.

In an embodiment, the transform skipped block contains only the regionand A is equal to W×H of the transform skipped block, where W is a widthof the transform skipped block and H is a height of the transformskipped block.

In an embodiment, the transform skipped block is divided into aplurality of regions including the region, and the maximum number ofcontext coded bins for each of the plurality of regions of the transformskipped block is B×A, where B is a positive number and A is a number ofquantized residues in the each of the plurality of regions.

In an embodiment, a method of video coding at a decoder is provided. Inthe method, a coded video bit stream is received. An indicator isreceived. The indicator indicates whether at least one of a currentblock and a neighboring block of the coded video bit stream is codedwith block differential pulse-code modulation (BDPCM). The current blockis adjacent to the neighboring block. When the at least one of thecurrent block and the neighboring block is indicated as being coded withBDPCM, a boundary strength is determined to be applied to a boundarybetween a current sub-block in the current block and a neighboringsub-block in the neighboring block, and deblocking is performed on theboundary between the current sub-block in the current block and theneighboring sub-block in the neighboring block using a deblocking filteraccording to the determined boundary strength.

In an embodiment, the neighboring sub-block is not coded with BDPCM.

In an embodiment, when the neighboring sub-block is coded with BDPCM,the boundary strength of the deblocking filter is determined to be 1 or2.

In an embodiment, when the current and neighboring sub-blocks are codedwith BDPCM, the deblocking is performed on the boundary between thecurrent sub-block in the current block and the neighboring sub-block inthe neighboring block based on a determination that a difference inquantization parameters between the current sub-block and theneighboring sub-block is greater than a threshold.

In an embodiment, when the current and neighboring sub-blocks are codedwith BDPCM, the deblocking is performed on the boundary between thecurrent sub-block in the current block and the neighboring sub-block inthe neighboring block based on a determination that the currentsub-block and the neighboring sub-block are coded with different BDPCMprediction modes.

In an embodiment, when the current and neighboring sub-blocks are codedwith BDPCM, the deblocking is performed on the boundary between thecurrent sub-block in the current block and the neighboring sub-block inthe neighboring block based on a determination that at least one of thecurrent sub-block and the neighboring sub-block has non-zerocoefficients.

Aspects of the disclosure also provide non-transitory computer-readablestorage mediums storing instructions which when executed by a computercause the computer to perform any of the above methods.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows a flowchart of an exemplary process for determining aboundary strength value according to an embodiment of the disclosure.

FIG. 9A shows examples of block differential pulse-code modulation(BDPCM) coded blocks according to an embodiment.

FIG. 9B shows examples of BDPCM coded blocks according to an embodiment.

FIG. 10A shows an exemplary context-based adaptive binary arithmeticcoding (CABAC) based entropy encoder in accordance with an embodiment.

FIG. 10B shows an exemplary CABAC based entropy decoder in accordancewith an embodiment.

FIG. 11 shows an exemplary CABAC based entropy encoding process inaccordance with an embodiment.

FIG. 12 shows an exemplary CABAC based entropy decoding process inaccordance with an embodiment.

FIG. 13 shows a flow chart outlining an entropy decoding process inaccordance with an embodiment.

FIG. 14 shows a flow chart outlining a deblocking filtering process inaccordance with an embodiment.

FIG. 15 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

I. Video Coding Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, whichcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information to include the QuantizerParameter (QP), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Boundary Strength Derivation in Deblocking

In HEVC, a deblocking filtering process is performed for each CU in thesame order as the decoding process. Vertical edges are first filtered(horizontal filtering) and then horizontal edges are filtered (verticalfiltering). When 8×8 block boundaries are determined to be filtered,filtering may be applied to the 8×8 block boundaries both for luma andchroma components. 4×4 block boundaries may not be processed in order toreduce the complexity. A boundary strength (Bs) can be used to indicatea degree or strength of a deblocking filtering process that may be usedfor a boundary. In an embodiment, a value of 2 for Bs indicates strongfiltering, 1 indicates weak filtering, and 0 indicates no deblockingfiltering.

In an embodiment, Bs is calculated on a 4×4 sample grid basis, but canbe re-mapped to an 8×8 sample grid. In an example, an 8×8 block includesfour 4×4 blocks, so a boundary of the 8×8 block includes two sides oftwo adjacent 4×4 blocks. The maximum of the two values of Bs whichcorrespond to 8 pixels forming a line in the 4×4 grid can be selected asthe Bs for boundaries in the 8×8 grid.

FIG. 8 shows a flowchart of an exemplary process (800) for determining aBs value according to an embodiment of the disclosure. It is noted thatthe order of the steps in FIG. 8 can be reordered or one or more stepsomitted in other embodiments.

In FIG. 8 , P and Q are two adjacent blocks with a boundary betweenthem. In a vertical edge case, P can represent a block located to theleft of the boundary and Q can represent a block located to the right ofthe boundary. In a horizontal edge case, P can represent a block locatedabove the boundary and Q can represent a block located below theboundary.

As shown in FIG. 8 , a Bs value can be determined based on a predictionmode (e.g., intra coding mode), a non-zero transform coefficient (e.g.,existence of non-zero transform coefficients), a reference picture, anumber of motion vectors, and a motion vector difference.

At step (S810), the process (800) determines whether P or Q is coded inan intra prediction mode. When at least one of P and Q is determined tobe coded in the intra prediction mode, the process (800) determines afirst value (e.g., 2) for the Bs. Otherwise, the process (800) proceedsto step (S820).

At step (S820), the process (800) determines whether P or Q has anon-zero transform coefficient. When at least one of P and Q isdetermined to have a non-zero transform coefficient, the process (800)determines a second value (e.g., 1) for the Bs. Otherwise, the process(800) proceeds to step (S830).

At step (S830), the process (800) determines whether P and Q havedifferent reference pictures. When P and Q are determined to havedifferent reference pictures, the process (800) determines a third value(e.g., 1) for the Bs. Otherwise, the process (800) proceeds to step(S840).

At step (S840), the process (800) determines whether P and Q havedifferent numbers of motion vectors. When P and Q are determined to havedifferent numbers of motion vectors, the process (800) determines afourth value (e.g., 1) for the Bs. Otherwise, the process (800) proceedsto step (S850).

At step (S850), the process (800) determines whether a motion vectordifference between P and Q is above or equal to a threshold T. When themotion vector difference between P and Q is determined to be above orequal to the threshold T, the process (800) determines a fifth value(e.g., 1) for the Bs. Otherwise, the process (800) determines a sixthvalue (e.g., 0) for the Bs. In an embodiment, the threshold T is set to1 pixel. In an example, the MV precision is ¼ pixel and a value of theMV difference threshold can be set to 4. In another example, the MVprecision is 1/16 and the value of the MV difference can be set to 16.

III. Block Differential Pulse-Code Modulation Mode

Block differential pulse-code modulation (BDPCM) is an intra-coding toolthat uses a differential pulse-code modulation (DPCM) approach at theblock level. A bdpcm_flag may be transmitted at the CU level wheneverthe CU is a luma intra coded CU having each dimension smaller or equalto 32. This flag indicates whether regular intra coding or DPCM is usedand is encoded using a single Context-based adaptive binary arithmeticcoding (CABAC) context.

BDPCM may use the Median Edge Detector of LOCO-I (e.g., used inJPEG-LS). Specifically, for a current pixel X having pixel A as a leftneighbor, pixel B as a top neighbor, and C as a top-left neighbor, theprediction of the current pixel X P(X) is determined by the followingformula:

P(X)= min(A, B) if C ≥ max(A, B) max(A, B) if C ≤ min(A, B) A + B − Cotherwise.

The pixel predictor uses unfiltered reference pixels when predictingfrom the top row and left column of the CU. The predictor then usesreconstructed pixels for the rest of the CU. Pixels are processed inraster-scan order inside the CU. The prediction error may be quantizedin the spatial domain, after rescaling, in a way identical to thetransform skip quantizer. Each pixel can be reconstructed by adding thedequantized prediction error to the prediction. Thus, the reconstructedpixels can be used to predict the next pixels in raster-scan order.Amplitude and signs of the quantized prediction error are encodedseparately. A cbf_bdpcm_flag is also coded. If cbf_bdpcm_flag is equalto 0, all amplitudes of the block are to be decoded as zero. Ifcbf_bdpcm_flag is equal to 1, all amplitudes of the block are encodedindividually in raster-scan order. In order to keep complexity low, theamplitude can be limited to at most 31 (inclusive). The amplitude may beencoded using unary binarization, with three contexts for the first bin,then one context for each additional bin until the 12th bin, and onecontext for all remaining bins. A sign may be encoded in bypass modelfor each zero residue.

In order to maintain the coherence of the regular intra mode prediction,the first mode in the most probable mode (MPM) list of the intra modeprediction is associated with a BDPCM CU (without being transmitted) andis available for generating the MPM for subsequent blocks.

The deblocking filter may be deactivated on a border/boundary betweentwo BDPCM coded blocks because neither of the BDPCM coded blocksperforms a transform, which is usually responsible for blockingartifacts. Further, BDPCM may not use any other step except the onesdescribed here. In particular, BDPCM may not perform any transform inresidual coding as described above.

Several tests regarding BDPCM have been conducted to investigate thethroughput improvements of BDPCM and the interaction with other ScreenContent Coding (SCC) tools.

FIG. 9A shows examples of BDPCM coded blocks according to an embodiment.The examples shown in FIG. 9A are related to Test 1. As shown in FIG.9A, in order to increase throughput, smaller blocks (e.g., having sizesof 4×4, 4×8, and 8×4) may be divided into two independently decodableareas, using a diagonal which effectively divides the block into twohalves (e.g., stair-case shaped partition).

In an embodiment, pixels from one area of a first half may not beallowed to use pixels from another area of a second half to compute theprediction. If pixels from one area need to use pixels from another areato compute the prediction, reference pixels are used instead. Forexample, the pixels from the other area may be replaced by the closestreference pixels. For example, a left neighbor may be replaced with aleft reference pixel from the same row, a top neighbor may be replacedwith a left reference pixel from the same column, and a top-leftneighbor may be replaced with the closest reference pixel. Thus, the twoareas can be processed in parallel.

FIG. 9A also provides an exemplary throughput of each block having adifferent size. For example, for a 4×4 block with two independentlydecodable areas, the throughput may be 4 pixels per cycle. For a 4×8 or8×4 block with two independently decodable areas, the throughput may be5.33 pixels per cycle. For an 8×8 block without independently decodableareas, the throughput may be 4.26 pixels per cycle. For an 8×8 blockwithout independently decodable areas, the throughput may be 4.26 pixelsper cycle. For a 16×16 block without independently decodable areas, thethroughput may be 8.25 pixels per cycle.

FIG. 9B shows examples of BDPCM coded blocks according to an embodiment.The examples shown in FIG. 9B are related to Test 2. In FIG. 9B, theblock may be divided using a vertical or horizontal predictor to replacea JPEG-LS predictor. The vertical or horizontal predictor may be chosenand signaled at a block level. The shape of the independently decodableregions reflects the geometry of the predictor. Due to the shape of thehorizontal or vertical predictors, which use a left or a top pixel forprediction of the current pixel, the most throughput-efficient way ofprocessing the block can be to process all the pixels of one column orrow in parallel, and to process these columns or rows sequentially. Forexample, in order to increase throughput, a block of width 4 is dividedinto two halves with a horizontal boundary when the predictor chosen onthis block is vertical, and a block of height 4 is divided into twohalves with a vertical boundary when the predictor chosen on this blockis horizontal. For a 4×4 block, an 8×4, or a 4×8 block with twoindependently decodable areas, the throughput may be 8 pixels per cycle.For a 4×8 block, an 8×4 block, or an 8×8 block without independentlydecodable areas, the throughput may be 8 pixels per cycle. For a 16×16block without independently decodable areas, the throughput may be 16pixels per cycle.

In Test 3, according to an embodiment of the present disclosure, theBDPCM residue amplitude is limited to 28, and the amplitude is encodedwith truncated unary binarization for the first 12 bins, followed byorder-2 Exp-Golomb equal probability bins for the remainder (e.g., usingan encodeRemAbsEP( ) function).

IV. Transform Coefficient Coding

Entropy coding can be performed at a last stage of video coding (or afirst stage of video decoding) after a video signal is reduced to aseries of syntax elements. Entropy coding can be a lossless compressionscheme that uses statistic properties to compress data such that anumber of bits used to represent the data are logarithmicallyproportional to the probability of the data. For example, by performingentropy coding over a set of syntax elements, bits representing thesyntax elements (referred to as bins) can be converted to fewer bits(referred to as coded bits) in a bit stream. CABAC is one form ofentropy coding. In CABAC, a context model providing a probabilityestimate can be determined for each bin in a sequence of bins based on acontext associated with the respective bin. Subsequently, a binaryarithmetic coding process can be performed using the probabilityestimates to encode the sequence of bins to coded bits in a bit stream.In addition, the context model is updated with a new probabilityestimate based on the coded bin.

FIG. 10A shows an exemplary CABAC based entropy encoder (1000A) inaccordance with an embodiment. For example, the entropy encoder (1000A)can be implemented in the entropy coder (545) in the FIG. 5 example, orthe entropy encoder (625) in the FIG. 6 example. The entropy encoder(1000A) can include a context modeler (1010) and a binary arithmeticencoder (1020). In an example, various types of syntax elements areprovided as input to the entropy encoder (1000A). For example, a bin ofa binary valued syntax element can be directly input to the contextmodeler (1010), while a non-binary valued syntax element can bebinarized to a bin string before bins of the bin string are input to thecontext modeler (1010).

In an example, the context modeler (1010) receives bins of syntaxelements, and performs a context modeling process to select a contextmodel for each received bin. For example, a bin of a binary syntaxelement of a transform coefficient in a transform block is received. Thetransform block may be a transform skipped block when the current blockis coded with BDPCM for prediction. A context model can accordingly bedetermined for this bin based, for example, on a type of the syntaxelement, a color component type of the transform component, a locationof the transform coefficient, and previously processed neighboringtransform coefficients, and the like. The context model can provide aprobability estimate for this bin.

In an example, a set of context models can be configured for one or moretypes of syntax elements. Those context models can be arranged in acontext model list (1002) that is stored in a memory (1001) as shown inFIG. 10A. Each entry in the context model list (1002) can represent acontext model. Each context model in the list can be assigned an index,referred to as a context model index, or context index. In addition,each context model can include a probability estimate, or parametersindicating a probability estimate. The probability estimate can indicatea likelihood of a bin being 0 or 1. For example, during the contextmodeling, the context modeler (1010) can calculate a context index for abin, and a context model can accordingly be selected according to thecontext index from the context model list (1002) and assigned to thebin.

Moreover, probability estimates in the context model list can beinitialized at the start of the operation of the entropy encoder(1000A). After a context model in the context model list (1002) isassigned to a bin and used for encoding the bin, the context model cansubsequently be updated according to a value of the bin with an updatedprobability estimate.

In an example, the binary arithmetic encoder (1020) receives bins andcontext models (e.g., probability estimates) assigned to the bins, andaccordingly performs a binary arithmetic coding process. As a result,coded bits are generated and transmitted in a bit stream.

FIG. 10B shows an exemplary CABAC based entropy decoder (1000B) inaccordance with an embodiment. For example, the entropy decoder (1000B)can be implemented in the parser (420) in the FIG. 4 example, or theentropy decoder (771) in the FIG. 7 example. The entropy decoder (1000B)can include a binary arithmetic decoder (1030), and a context modeler(1040). The binary arithmetic decoder (1030) receives coded bits from abit stream, and performs a binary arithmetic decoding process to recoverbins from the coded bits. The context modeler (1040) can operatesimilarly to the context modeler (1010). For example, the contextmodeler (1040) can select context models in a context model list (1004)stored in a memory (1003), and provide the selected context models tothe binary arithmetic decoder (1030). The context modeler (1040) candetermine the context models based on the recovered bins from the binaryarithmetic decoder (1030). For example, based on the recovered bins, thecontext modeler (1040) can know a type of a syntax element of a nextto-be-decoded bin, and values of previously decoded syntax elements.That information is used for determining a context model for the nextto-be-decoded bin.

V. Limitations on a Number of Context Coded Bins

As described above, the residue associated with each pixel may bebinarized to a bin representing its sign and a series of binsrepresenting its absolute value. The absolute value may be quantized sothat it is less than or equal to a given number (e.g., 31 or 28). One ormore context models, or the equal probability (EP) model (i.e., bypassmodel), can be associated with each bin. For each residual symbol, up to13 bins may be associated with one or more context models. The largenumber of context coded bins (e.g., bins that associated with at least acontext model) may decrease the throughput of the entropy encoder ordecoder during syntax coding, and it may become a burden for certaincodec implementations (e.g., some hardware codecs). Therefore, setting amaximum number of context coded bins can, for example, not only boostthe coding speed, but also reduce required memory size and cost ofmaintaining those context models.

Accordingly, aspects of the disclosure include methods for limiting thenumber of context coded bins used for transform coefficient entropycoding. For example, in the BDPCM mode, a number of bins in the binaryrepresentation of the quantized residue can be associated with a contextmodel. One or more limitations are placed on the number of bins that areassociated with the context model in some embodiments.

A W×H block may be virtually divided into a plurality of sub-regions. Asubset of the plurality of sub-regions may be coded with BDPCM inparallel with each other. In an example, each of the plurality ofsub-regions may be coded with BDPCM in parallel with each other. The W×Hblock may be a transform block or a transform skipped block. The maximumnumber of context coded bins (e.g., MaxCcbs) for each sub-region may beset to B×A, where A is the number of quantized residues in thesub-region, and B is a positive number. B may or may not be signaled inthe bit stream, for example from the encoder to the decoder. When thenumber of bins in the sub-region does not exceed a limit (e.g., B×A),each of the bins in the sub-region can be coded with a context model.When the number of bins in the sub-region exceeds this limit, theremaining bins that are not to be context coded may be coded with adifferent model (e.g., an EP model).

In an embodiment, B is the same for luma and chroma components. Forexample, B=2. In an embodiment, B is different for luma and chromacomponents. For example, B=2 for luma components, and B=1 for chromacomponents.

In an embodiment, B can be a fractional number, such as 0.5 or 1.2. Insome examples, B depends on A. A is the number of quantized residues inthe sub-region, as defined above. For example, when A is less than athreshold, B may be equal to a specific value (e.g., 1). Otherwise, Bmay be equal to another value (e.g., 2). The threshold can be, forexample, 4, 8, 16, 32, 64, 128, or 256.

In an embodiment, B may be determined based on two thresholds. Forexample, when A is less than a first threshold, B may be equal to afirst value (e.g., 1). When A is equal to or larger than a secondthreshold, B may be equal to a second value (e.g., 2). As an example,the first and second thresholds could be any one of the followingvalues: 4, 8, 16, 32, 64, 128, and/or 256.

In an embodiment, B may be determined based on more than two (e.g.,three) thresholds in a similar way as described above. For example, whenA is less than a first threshold, B may be equal to a first value (e.g.,0.5). When A is equal to or larger than a first threshold and less thana second threshold, B may be equal to a second value (e.g., 1). When Ais equal to or larger than a third threshold, B may be equal to a thirdvalue (e.g., 2). As an example, the first, second, and third thresholdscould be any one of the following values: 4, 8, 16, 32, 64, 128, and/or256.

In an embodiment, the W×H block is not divided into sub-regions andcontains only one region. The maximum number of context coded bins forthe region may also be set to be B×A. In this case, A may be equal toW×H, B is a positive number, and the maximum number of context codedbins (e.g., MaxCcbs) is equal to B×W×H. When the number of bins in theblock does not exceed a limit (e.g., B×W×H), each of the bins in theblock can be coded with a context model. When the number of bins in theblock exceeds this limit, the remaining bins that are not to be contextcoded may be coded with a different model (e.g., an EP model).

In an embodiment, a W×H block is divided into H sub-regions and eachsub-region contains one row of W residues. In this case, A may be equalto W, and the maximum number of context coded bins (e.g., MaxCcbs) foreach row is equal to B×W. When the number of bins in the row does notexceed a limit (e.g., B×W), each of the bins in the row can be codedwith a context model. When the number of bins in the row exceeds thislimit, the remaining bins that are not associated with a context modelmay be coded with a different model (e.g., an EP model).

In an embodiment, a W×H block is divided into W sub-regions and eachsub-region contains one column of H residues. In this case, A may beequal to H, and the maximum number of context coded bins (e.g., MaxCcbs)for each column is equal to B×H. When the number of bins in thesub-region does not exceed a limit (e.g., B×H), each of the bins in thecolumn can be coded with a context model. When the number of bins in thecolumn exceeds this limit, the remaining bins that are not associatedwith a context model may be coded with a different model (e.g., an EPmodel).

In an embodiment, an arbitrary partition can be used to generate thesub-region such as the stair-case shaped partition described in FIG. 9A,or the horizontal/vertical split described in FIG. 9B. Further, morethan two partitions can be used in other embodiments described above.

FIG. 11 shows an exemplary method of coefficient encoding based on amaximum number of context coded bins. The maximum number of contextcoded bins may be set, for example, based on one or more of theembodiments described above.

As described above, bits representing the syntax elements (e.g., bins)can be converted into fewer bits in a bit stream by performing entropycoding on the syntax elements. In FIG. 11 , the quantized residue (1110)may be converted to a binary string (1120) using binary coding. Forexample, the converted binary string (1120) may be11010010001111100011101010010101010010101010111000111000101101011010101110.The binary string (1120) may include 4 segments and may represent 2syntax elements. The bins for the first syntax element is110100100011111000111010100101010, and the bins for the second syntaxelement is 10010101010111000111000101101011010101110. A CABAC basedentropy encoder, such as the entropy encoder (545) in FIG. 5 or theentropy encoder (625) in FIG. 6 , may perform context modeling on thebinary string based on a maximum number of context coded bins. Forexample, when both the width of the block W and the height of the blockH are equal to 4 and the block contains only one region, A is equal to4×4=16 and B may be set to be 2. Therefore, the maximum number ofcontext coded bins in the block is B×A=32. Accordingly, as shown in FIG.11 , when the number of context coded bins for this block (shown in boldand underscore font) does not reach 32 (as shown in the first 3 segmentsin the binary string), the entropy encoder is free to choose whether touse context modeling to code the bins, according to the BDPCM algorithm.When the maximum number of context coded bins (e.g., MaxCcbs) is reached(as shown in the fourth segment), the remaining bins cannot be codedwith context modeling. Instead, the bins may be coded with an EP model.In some examples, the entropy encoder may include a counter and thecounter counts the number of context coded bins. The counter output maybe initially set as 0 and may count from 0 to the maximum number ofcontext coded bins. When the counter reaches the maximum number ofcontext coded bins, the remaining bins may not be coded with contextmodeling.

In an embodiment, when both the width of the block W and the height ofthe block H equal to 8 and the block is split into 4 sub-regions withthe same size. Each sub-region has a size of 4×4. Therefore, A is equalto 16. In this case, B may be 2 and the maximum number of context codedbins is 32. Accordingly, the example described in FIG. 11 can also beapplied in this embodiment.

FIG. 12 shows an exemplary method of coefficient decoding based on amaximum number of context coded bins. A CABAC based entropy decoder maybe provided in accordance with an embodiment. The entropy decoder can beimplemented in the parser (420) in the FIG. 4 example, or the entropydecoder (771) in the FIG. 7 example. As described above, the binaryarithmetic decoder of the entropy decoder receives coded bits (1210)from a bit stream, and performs a binary arithmetic decoding process torecover bins (1220) from the coded bins. Similar to the entropy encoder,the entropy decoder can also determine a maximum number of context codedbins based on the size of the block or the divided sub-regions. Forexample, when both of the width of the block W and the height of theblock H are equal to 4 and the block contains only one region, A isequal to 16 and B may be 2. Therefore, the maximum number of contextcoded bins is B×A=32. Accordingly, as shown in FIG. 12 , when the numberof context coded bins for this block (shown in bold and underscore font)does not reach 32 (as shown in the first 3 segments in the binarystring), the entropy decoder is free to choose whether to use contextmodeling to decode the coded bins, according to the BDPCM algorithm.When the maximum number of context coded bins is reached (as shown inthe fourth segment), the bins cannot be decoded with context modeling.Instead, the bins are decoded with an EP model. The decoded binarystring (1220) may be converted to a quantized residue (1230) using adebinarization process.

VI. Application of a Deblocking Filter on BDPCM Coded Blocks

As described above, the deblocking filter may be deactivated on a borderbetween two BDPCM coded blocks because, for example, neither of theBDPCM coded blocks performs a transform that causes blocking artifacts.In order to avoid or minimize block artifacts, a deblocking filter maybe applied between two blocks where at least one of block is coded inBCPCM to avoid or minimize the perceptual artifacts.

In an embodiment, a deblocking filter may be always activated ordeactivated between a BDPCM coded block and a non-BDPCM coded block. Insome examples, a boundary strength (Bs) is set to a fixed value betweena BDPCM coded block and a non-BDPCM coded block. The fixed value couldbe 0, 1 or 2. For example, the value 0 indicates that the deblockingfilter is deactivated, 1 indicates that weak filtering is applied, and 2indicates that strong filtering is applied.

In an embodiment, a deblocking filter may be always activated betweentwo adjacent BDPCM coded blocks. The Bs may be set to be differentvalues according to the prediction modes of the two BDPCM coded blocks.In some examples, when one block is coded in horizontal BDPCM and theother block is coded in vertical BDPCM, Bs is set to be 2. In otherexamples, when both blocks are coded using horizontal prediction, Bs isset to be 1.

In some embodiments, a deblocking filter may be conditionally activatedbetween two adjacent BDPCM coded blocks. In some examples, thedeblocking filter is activated only when the difference in QPs of thetwo adjacent BDPCM coded blocks is greater than a threshold. Thethreshold can be 0, 1, 2, or 3, for example.

In some examples, a deblocking filter is activated only when the twoBDPCM coded blocks have different prediction modes. For example, whenone block is coded in horizontal BDPCM and the other block is coded invertical BDPCM, the deblocking filter is activated.

In some examples, BDPCM is not regarded as an intra mode in the boundarystrength derivation between two adjacent BDPCM modes. The reference andMV checks in the boundary strength derivation are skipped for the twoadjacent BDPCM blocks. For example, when the boundary strengthderivation process described in FIG. 8 is applied, and at least one ofthe two adjacent BDPCM coded blocks has a non-zero coefficient, Bs isset to 1 and the deblocking filter is activated. When neither of the twoadjacent BDPCM coded blocks has a non-zero coefficient, Bs is set to be0 and the deblocking filter is deactivated.

VII. Exemplary Decoding Processes

FIG. 13 shows a flow chart outlining an entropy decoding process (1300)according to some embodiments of the disclosure. The process (1300) canbe used in entropy decoding of several types of transform coefficientsyntax elements based on a maximum number of context coded binsdisclosed herein. In various embodiments, the process (1300) can beexecuted by processing circuitry, such as the processing circuitry inthe terminal devices (210), (220), (230) and (240), the processingcircuitry that performs functions of the video decoder (310), theprocessing circuitry that performs functions of the video decoder (410),and the like. In some embodiments, the process (1300) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1300). The process starts at (S1301) and proceeds to (S1310).

At (S1310), a bit stream including coded bits can be received. The codedbins can be coded from bins of various types of syntax elementscorresponding to residues of a transform skipped block in a codedpicture. For example, the various types of syntax elements can includesignificance syntax elements, parity syntax elements, greater than 1syntax elements, and/or greater than 2 syntax elements. The significantsyntax elements (e.g., sig_coeff_flag) may indicate that an absolutevalue of the current transform coefficient (absLevel) is greater than 0.The parity syntax elements (e.g., par_level_flag) may indicate theparity of absLevel. The greater than 1 syntax elements (e.g.,rem_abs_gt1_flag) may indicate that absLevel−1 is greater than 0. Thegreater than 2 syntax elements (e.g., rem_abs_gt2_flag) may indicatethat absLevel−4 is greater than 0. The transform skipped block mayindicate that a transform was not be performed on the transform block.For example, when the current block is coded with BDPCM, a transform isnot performed on the transform block.

At (S1320), context modeling can be performed to determine a contextmodel for each of a number of the bins of syntax elements of the region.The number of the bins of syntax elements that are context coded may notexceed a maximum number of context coded bins set for the region. Thenumber of the bins of syntax elements is less than or equal to a totalnumber of the bins of syntax elements for the region of the transformskipped block. The maximum number of context coded bins can bedetermined according to one or more of the embodiments described above.For example, the maximum number of context coded bins (e.g., MaxCcbs)for the region of the transform skipped block is set to be B×A, where Bis a positive number and A is a number of quantized residues in theregion. B can be a predetermined number such as an integer or afractional number. Alternatively, B can depend on A. B may be signaledfrom the encoder to the decoder so the decoder can also determine themaximum number of context coded bins of B×A.

At (S1330), the coded bits of the number of the bins of syntax elementscan be decoded based on the determined context models. The coded bits ofthe remaining total number of the bins of syntax elements for the regionof the transform skipped block may be decoded based on an EP model(i.e., a bypass model). Based on the recovered bins, transformcoefficient levels of the transform coefficients can be reconstructed.The process (1300) proceeds to and terminates at (S1399).

FIG. 14 shows a flow chart outlining a deblocking filtering process(1400) according to some embodiments of the disclosure. The process(1400) can be used when at least one of a current block and aneighboring block of the coded video bitstream is coded with blockdifferential pulse-code modulation (BDPCM). In various embodiments, theprocess (1400) can be executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videodecoder (310), the processing circuitry that performs functions of thevideo decoder (410), and the like. In some embodiments, the process(1400) is implemented in software instructions, thus when the processingcircuitry executes the software instructions, the processing circuitryperforms the process (1400). The process starts at (S1401) and proceedsto (S1410).

At (S1410), a bit stream including coded bits can be received.

At (S1420), an indicator can be received from the encoder. The indicatormay indicate whether at least one of a current block and a neighboringblock of the coded video bit stream is coded with block differentialpulse-code modulation (BDPCM). The current block may be adjacent to theneighboring block. The current block is in the current CU and theneighboring block may be in the same CU or may be in another CU adjacentto the current CU. As described above, a bdpcm_flag may be transmittedat the CU level whenever the CU is a luma intra CU having a dimensionsmaller or equal to 32. Therefore, when the bdpcm_flag received by thedecoder indicates that the CU is coded with BDPCM, the current block iscoded with BDPCM. Therefore, at least one of the current block in the CUand the neighboring block of the received coded video bit stream iscoded with BDPCM. Similarly, when the bdpcm_flag received by the decoderindicates that another CU is coded with BDPCM and the neighboring blockis in the other CU, the neighboring block is coded with BDPCM.Therefore, at least one of the current block in the CU and theneighboring block in the other CU of the received coded video bit streamis coded with BDPCM.

At (S1430), the process (1400) determines whether the at least one ofthe current block and the neighboring block is indicated as being codedwith BDPCM. When the at least one of the current block and theneighboring block is indicated as being coded with BDPCM, the process(1400) proceeds to step (S1440).

At (S1440), a boundary strength (Bs) can be determined to be applied toa boundary between a current sub-block in the current block and aneighboring sub-block in the neighboring block.

At (S1450), deblocking can be performed on the boundary between thecurrent sub-block in the current block and the neighboring sub-block inthe neighboring block using a deblocking filter according to thedetermined boundary strength. The deblocking filter can be appliedaccording to one or more of the embodiments described above.

For example, when the at least one of the current block and theneighboring block is indicated as being coded with BDPCM, a deblockingfilter may always be activated or deactivated between the a currentsub-block in the current block and a neighboring sub-block in theneighboring block. A Bs can be determined to be applied to a boundarybetween a current sub-block in the current block and a neighboringsub-block in the neighboring block. The current sub-block in the currentblock and the neighboring sub-block in the neighboring block may beadjacent to each other. When the determination of the Bs uses themethods described in FIG. 8 , the Bs is determined to be a fixed valueof 2 in a case that at least one of the current sub-block in the currentblock and the neighboring sub-block in the neighboring block is intracoded. In an embodiment, the determination of the Bs may not use themethods described in FIG. 8 . Instead, the Bs may be determined to be aflexible value such as 0, 1, or 2.

In an embodiment, when the neighboring sub-block in the neighboringblock is also coded with BDPCM, a deblocking filter may be alwaysactivated between the current sub-block and the neighboring sub-block.

In an embodiment, when the neighboring sub-block in the neighboringblock is also coded with BDPCM, a deblocking filter may be conditionallyactivated between the current sub-block and the neighboring sub-block.The conditions may include the difference in QPs between the twosub-blocks, the prediction modes of the current block and neighboringblock, and whether BDPCM is considered as an intra mode when determiningthe Bs according to the methods described in FIG. 8 .

The process (1400) proceeds to and terminates at (S1499).

VIII. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 15 shows a computersystem (1500) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 15 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1500).

Computer system (1500) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1501), mouse (1502), trackpad (1503), touchscreen (1510), data-glove (not shown), joystick (1505), microphone(1506), scanner (1507), camera (1508).

Computer system (1500) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1510), data-glove (not shown), or joystick (1505), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1509), headphones(not depicted)), visual output devices (such as screens (1510) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1500) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1520) with CD/DVD or the like media (1521), thumb-drive (1522),removable hard drive or solid state drive (1523), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1500) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1549) (such as, for example USB ports of thecomputer system (1500)); others are commonly integrated into the core ofthe computer system (1500) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1500) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1540) of thecomputer system (1500).

The core (1540) can include one or more Central Processing Units (CPU)(1541), Graphics Processing Units (GPU) (1542), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1543), hardware accelerators for certain tasks (1544), and so forth.These devices, along with Read-only memory (ROM) (1545), Random-accessmemory (1546), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1547), may be connectedthrough a system bus (1548). In some computer systems, the system bus(1548) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1548),or through a peripheral bus (1549). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1541), GPUs (1542), FPGAs (1543), and accelerators (1544) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1545) or RAM (1546). Transitional data can be also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1500), and specifically the core (1540) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1540) that are of non-transitorynature, such as core-internal mass storage (1547) or ROM (1545). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1540). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1540) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1546) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1544)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit DPCM: Differential Pulse-codeModulation BDPCM: Block Differential Pulse-code Modulation SCC: ScreenContent Coding Bs: Boundary Strength

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of video encoding performed in a videoencoder, the method comprising: performing context modeling to determinea context model for each of a number of bins of syntax elementscorresponding to residues of a region of a transform skipped block in acoded picture, the transform skipped block being coded with BlockDifferential Pulse-code Modulation (BDPCM) and divided into a pluralityof regions, the number of the bins of syntax elements being contextcoded not exceeding a maximum number of context coded bins set for theregion, the maximum number of context coded bins being determined basedon a comparison between a threshold and a number of quantized residuesin the region; and generating a bit stream including coded bits of thebins of syntax elements based on the determined context models.
 2. Themethod of claim 1, wherein the maximum number of context coded bins forthe region of the transform skipped block is B×A, where A is the numberof quantized residues in the region and B is a positive number that isbased on the number of quantized residues in the region indicated by A.3. The method of claim 1, wherein the number of the bins of syntaxelements that are context coded is less than or equal to a total numberof the bins of syntax elements for the region of the transform skippedblock.
 4. The method of claim 3, wherein the generating comprises:generating the coded bits of the number of the bins of syntax elementsthat are context coded based on the determined context models; andgenerating the coded bits of the remaining total number of the bins ofsyntax elements that are not context coded for the region of thetransform skipped block based on an equal probability model.
 5. Themethod of claim 1, wherein B is an integer.
 6. The method of claim 1,wherein B is a fractional number.
 7. The method of claim 1, wherein B isa first number when A is greater than the threshold and B is a secondnumber when A is not greater than the threshold.
 8. The method of claim1, wherein the maximum number of context coded bins for each of theplurality of regions of the transform skipped block is B×A.
 9. Anapparatus of video encoding, comprising: processing circuitry configuredto: perform context modeling to determine a context model for each of anumber of bins of syntax elements corresponding to residues of a regionof a transform skipped block in a coded picture, the transform skippedblock being coded with Block Differential Pulse-code Modulation (BDPCM)and divided into a plurality of regions, the number of the bins ofsyntax elements being context coded not exceeding a maximum number ofcontext coded bins set for the region, the maximum number of contextcoded bins being determined based on a comparison between a thresholdand a number of quantized residues in the region; and generate a bitstream including coded bits of the bins of syntax elements based on thedetermined context models,
 10. The apparatus of claim 9, wherein themaximum number of context coded bins for the region of the transformskipped block is B×A, where A is the number of quantized residues in theregion and B is a positive number that is based on the number ofquantized residues in the region indicated by A.
 11. The apparatus ofclaim 9, wherein the number of the bins of syntax elements that arecontext coded is less than or equal to a total number of the bins ofsyntax elements for the region of the transform skipped block.
 12. Theapparatus of claim 11, wherein the processing circuitry is furtherconfigured to: generate the coded bits of the number of the bins ofsyntax elements that are context coded based on the determined contextmodels; and generate the coded bits of the remaining total number of thebins of syntax elements that are not context coded for the region of thetransform skipped block based on an equal probability model.
 13. Theapparatus of claim 9, wherein B is an integer.
 14. The apparatus ofclaim 9, wherein B is a fractional number.
 15. The apparatus of claim 9,wherein B is a first number when A is greater than the threshold and Bis a second number when A is not greater than the threshold.
 16. Theapparatus of claim 9, wherein the maximum number of context coded binsfor each of the plurality of regions of the transform skipped block isB×A.
 17. A non-transitory computer-readable storage medium storinginstructions which when executed by a processor cause the processor toperform: performing context modeling to determine a context model foreach of a number of bins of syntax elements corresponding to residues ofa region of a transform skipped block in a coded picture, the transformskipped block being coded with Block Differential Pulse-code Modulation(BDPCM) and divided into a plurality of regions the number of the binsof syntax elements being context coded not exceeding a maximum number ofcontext coded bins set for the region, the maximum number of contextcoded bins being determined based on a comparison between a thresholdand a number of quantized residues in the region; and generating a bitstream including coded bits of the bins of syntax elements based on thedetermined context models.
 18. The non-transitory computer-readablestorage medium of claim 17, wherein the maximum number of context codedbins for the region of the transform skipped block is B×A, where A isthe number of quantized residues in the region and B is a positivenumber that is based on the number of quantized residues in the regionindicated by A.
 19. The non-transitory computer-readable storage mediumof claim 17, wherein the number of the bins of syntax elements that arecontext coded is less than or equal to a total number of the bins ofsyntax elements for the region of the transform skipped block.
 20. Thenon-transitory computer-readable storage medium of claim 19, wherein thegenerating comprises: generating the coded bits of the number of thebins of syntax elements that are context coded based on the determinedcontext models; and generating the coded bits of the remaining totalnumber of the bins of syntax elements that are not context coded for theregion of the transform skipped block based on an equal probabilitymodel.